This invention relates to pin arrangements used in cone synchronizers to facilitate shifting between high and low ranges in a multispeed transmission.
In the prior art, heavy vehicle transmissions typically consist of two sections. A first main section includes a plurality of selectable gears to provide different speed ratios. A second auxiliary section takes an input from the first section and modifies the speed to provide a multiple of additional speeds. Auxiliary sections include both range and splitter sections.
The range section shifts the speeds within the main transmission section between two ranges, namely high and low. The background will be explained with reference to a range section, but it should be understood it may also apply to splitter sections. Known range sections move a shift collar to connect an input shaft directly to an output shaft, thereby creating a high speed. Alternatively, the collar connects the input to a gear reduction to drive the output shaft to provide the low function.
A synchronizer may be associated with both the high and low range positions to assist the transmission in beginning to move the gears to the desired speed just prior to engagement. The synchronizer includes a first and second cone in spaced relationship with the shift collar interposed between. A plurality of pins couple the cones and the shift collar together so that they rotate as a group. When the shift collar is moved laterally from neutral into high or low range, the shift collar engages blocking surfaces on the pins and moves the corresponding cone to match the speeds of the input shaft and the corresponding gear.
Since pin length determines, in part, the length of the synchronizer and therefore the length of the transmission, it is desirable to utilize the shortest pin length possible. FIG. 1A depicts a prior art configuration utilizing preblocked pins 2, 4 while FIG. 1B depicts a prior art configuration utilizing preenergized pins 15. Reference will now be made to both the preblocked synchronizers and preenergized synchronizers simultaneously with preenergized synchronizer reference numerals in parentheses. These prior art configurations require that during a shift from one range to another (for example from left to right in the Figures), the shift collar disengages the large diameter surfaces 6 (16), then engages the small diameter surfaces 8, 12 (18), and engages the blocking surfaces 13 (19) thereby causing the cone 66 (66) to move to the right to synchronize a gear. Once synchronized, the shift collar engages the large diameter surfaces 11 (16).
Similarly when a shift is made from right to left, the shift collar disengages the large diameter surfaces 11 (16), then engages the small diameter surfaces 8, 12 (18), and engages the blocking surfaces 10 (19) thereby causing cone 42 (42) to move to the right to synchronize a gear. Once synchronized the shift collar engages the large diameter surfaces 6 (16).
By eliminating engagement of the shift collar with the small diameter surfaces in the neutral position between range shifts, the overall pin length may be reduced thereby reducing the length of the synchronizer and transmission.
In a preferred embodiment of this invention, a plural cone synchronizer is incorporated into an auxiliary section of a heavy vehicle transmission. First and second cones are in spaced relationship from one another and rotate about a common axis. A shift collar is interposed between the first and second cones and rotates about and is slidable along the axis to and from a neutral position. The shift collar has first and second sets of apertures therethrough which have engaging surfaces.
A plurality of preblocked pins interconnect the first and second cones. A first set of pins extend from the first cone through the first set of apertures. The first set of pins have first large diameter surfaces adjacent to the first cone and first small diameter surfaces opposite the first large diameter surfaces. First blocking surfaces are disposed between the first small and large diameter surfaces. Similarly, a second set of pins extend from the second cone through the second set of apertures. The second set of pins have second large diameter surfaces adjacent to the second cone and second small diameter surfaces opposite the second large diameter surfaces. Second blocking surfaces are disposed between the second small and large diameter surfaces.
The pins collectively have neutral surfaces that are engageable with the engaging surfaces when the shift collar is in the neutral position. The engaging surfaces are prevented from simultaneously engaging with the first and second small diameter surfaces in the neutral position because of the width of the engaging surfaces and the location of the first and second blocking surfaces relative to one another. In this way, the contact with the small diameters is eliminated when shifting between high and low range.
A method of shifting between a plurality of gears using the above preferred pin arrangement includes decoupling a first gear and a shaft by moving a synchronizer shift collar out of engagement with a set of first large diameter pin surfaces. The next step includes synchronizing a second gear and the shaft by moving the shift collar into engagement with a set of second blocking pin surfaces. Finally, the last step includes coupling the second gear and the shaft by moving the shift collar into engagement with a set of second large diameter pin surfaces.
These and other features of the present invention can be best understood from the following specification and drawings, of which the following is a brief description.